Valuable prior medical inventions pertaining to fluid flow (flow of liquids and gases) to and from a medial patient are acknowledged. Nevertheless, to some important extent, control of when and to what extent liquid and gas flow is permitted into and from a patient has been a long standing need in certain medical applications. Control of gas and liquid flow can be critical to the care for the patient. Flow of liquid to and from the patient includes but is not limited to infusion of intravenous liquid into the cardiovascular system and removal of blood samples. Flow of gas typically involves the respiratory system of the patient, including but not limited to preventing the patient from exhausting all gas within the lungs during exhalation, to thereby keep the air sacks in the lungs partially inflated and, therefore, continuously open. Control of gas and liquid flow can be critical to the care for the patient.
More specifically, in respect to liquid flow to the patient, it has long been recognized to be medically desirable to intravenously infuse a predetermined liquid into and to sample blood or other liquids from a patient. Typically, during delivery of IV solution to the patient through an infusion administration set comprising a cannula, such as a catheter tube or IV needle, it is difficult to accurately predict the point in time when the supply of IV solution will become exhausted. It is even more difficult to coordinate availability of nursing personnel to timely disable the IV administration set to prevent flow from a soon-to-be dry IV supply through the catheter tube or needle. As a consequence, the distal tip of the cannula sometimes experiences bleed-back and clotting. Also, as a container of IV solution progressively empties, a corresponding change in the hydraulic head takes place. As a consequence, a desired well regulated drip rate is not conventionally available.
More specifically, when a conventional IV administration set is connected to a patient, the flow of IV solution occurs because the force of gravity upon the solution in the elevated container exceeds the blood pressure in the cardiovascular system of the patient to the extent permitted by a manually-controlled drip mechanism. As the supply of IV solution is progressively used until exhausted, the pressure difference changes until there is no pressure component from the IV solution.
When the availability of IV solution is undesirably exhausted or low, the cardiovascular pressure prevails, causing blood flow into the IV catheter tube for a distance, which may vary depending on circumstances. Sometimes, this blood flow reaches, contaminates, and requires replacement of an IV filter, forming a part of the IV administration set. In any event, the aforesaid blood in the catheter will clot, within a short time. Subsequent negligent introduction of the clot into the bloodstream becomes a risk, which, if not discovered, places the patient at jeopardy. If timely discovered, replacement of the IV system is required.
Also, where the patient raises the venipuncture site above the IV container, refluxing or bleedback flow of blood into the distal end of the cannula sometimes occurs. This reflux may or may not reach the filter of the IV administration set, but, in either event, causes IV flow to stop, which results in clotting within either the cannula, the filter, or both. When and if discovered, both the clotted IV filter and catheter tube are replaced. This is disadvantageous because of accompanying patient trauma, expense, and risk. It is bad practice and an unacceptable risk to the patient to force a clot from the catheter tube into the bloodstream, but, due to negligence, this sometimes happens.
It is known to use a standard one-way outdwelling (outside the patient) valve to prevent undesired blood flow into the distal end of an indwelling cannula, such as a catheter tube or IV needle. This standard one-way valve will not allow blood sampling when the standard one-way valve is located between the catheter tube and the sampling site.
It has also been proposed that a two-way outdwelling slit valve (such as that disclosed in commonly owned U.S. Pat. No. 5,205,834) be used. With such a two-way outdwelling slit valve which has great medical value, the pressure requirements to open the slit valve are substantially fixed, i.e. built into the valve at the time of manufacture. The desired pressure requirement to open the slit valve in one direction of flow can be different than to open it in the other direction of flow.
Prior out-dwelling slit valves which are not readily adjustable, typically require a relatively high degree of manufacturing precision to ensure that the resulting valve opens in a given direction at the desired threshold.
In certain medical applications, it has been found desirable for outdwelling slit valves of the type disclosed in U.S. Pat. No. 5,205,834 be inventively extended into environments where the characteristics of the valves may be varied for control and adjustment purposes. For example. use of an outdwelling slit valve having variable characteristics in lieu of a mechanical drip controller, if inventively achieved would overcome or substantially alleviate the problems mentioned above concerning the IV administration sets.
Turning to flow of gases, proper respiratory care for the patient likewise requires precise control of the types and quantities of gases delivered to and expelled from the respiratory system of the intubated patient. When the patient is afflicted with some form of lung disease, the patient is typically placed on a respirator or ventilator. Sometimes controlled amounts of pure oxygen are cyclically delivered to the patient. Gas born medications are likewise sometimes introduced into the lungs on a controlled or metered basis. To prevent collapsing of the air sacks in the lungs, in the past, a C-PAP valve has been used to limit exhalation and prevent complete gas discharge from the lungs.
Reliability and precision of gas flow control devices, such as the C-PAP valve, for use with the respiratory system of a patient have presented persistent problems. Almost constant or regular intermittent overseeing has often been required by a medical provider in order to insure that errors and malfunction of such prior art gas flow control devices do not work adversely to the best interests of the patient.
There has long existed a need for a gas flow control which is precise, reliable, and unlike the present C-PAP valves, for example, does not require substantial on-going monitoring by a nurse or other medically trained person.